The present invention relates to a wire twisting device for use in a reinforcement binding machine and, in particular, to a wire twisting device for use in a reinforcement binding machine which is improved in reliability.
A reinforcement binding machine is generally well-known as a machine for binding reinforcements at their mutually intersecting positions thereof in a reinforcement arranging process in a reinforcement concrete construction work. FIG. 3 shows a conventional reinforcement binding machine 1 including a housing 2 in which a wire feed device 3 and a wire twisting device 4 are incorporated. On the side surface (in FIG. 3, the side surface is situated on the deep or far side of the sheet thereof) of the rear portion of the housing 2, there is pivotally and rotatably mounted a reel base (not shown) on which a wire reel can be mounted.
A feed roller 5, which is included in the wire feed device 3 and can be driven or rotated by a motor (not shown), supplies a wire wound around the wire reel through a guide pipe 6 to an arc-shaped nose portion 7 which is formed in the front portion of the reinforcement binding machine 1.
The wire twisting device 4 is used to bind a wire W which is wound around reinforcements R by the wire feed device 3, while the wire twisting device 4 drives or rotates a screw shaft 10, which is connected to a motor 8 through a reduction gear 9, in both forward and reverse directions.
As shown in FIG. 4, a slotted shaft 11 disposed coaxially with the screw shaft 10 is rotatably connected to the leading end of the screw shaft 10 by a flanged pin 12 and a removal preventive ring 13, while a guide pin 14 extending at right angles to the axis of the shaft 11 is provided on the leading end portion of a slot 11a formed in the shaft 11.
A sleeve nut 15 is mounted on the outside surface of the screw shaft 10 and, further, a sleeve 16 is fixed to the outer periphery of the sleeve nut 15. And, on the outer peripheral surface of the rear portion of the sleeve 16, there is arranged a rotation preventive fin 17 which is formed long in the axial direction thereof and extends in the radial direction of the sleeve 16. A pair of hook levers 18 are pivotally mounted on the two sides of the neighborhood of the leading end portion of a slot 16a formed in the front portion of the sleeve 16, in such a manner that they are opposed to each other with the shaft 11 between them. Guide grooves 18a which extend in the radial direction of the hook levers when viewed from the rotation shafts of the hook levers 18 are formed in the respective inner portions of the hook levers 18, while the guide grooves 18a are engaged with the guide pin 14 provided on the shaft 11.
The pair of hook levers 18 respectively include leading end hook portions 18b. And, the leading end hook portions 18b of the hook levers 18, when they are held in their wait/ready states, spread open and face forward. When the sleeve nut 15 and sleeve 16 are moved or slid forward on the shaft 11, the guide pin 14 is then moved backwardly or retreats with respect to the sleeve 16 and the inside portions of the hook levers 18 are thereby pulled backward, with the result that the leading end hook portions 18b of the two hook levers 18 are rotated in their mutually approaching directions and are finally made to cross each other.
The wire twisting device 4 is structured such that it takes its wait/ready position when the sleeve nut 15 and sleeve 16 are rotated 90.degree. from their positions shown in FIG. 3 and the pair of hook levers 18 are thereby moved to their horizontally held conditions and, in this wait/ready position, the wire loop W can be gripped from the two sides thereof, that is, from the left and right sides thereof.
The wire feed device 3 and wire twisting device 4 can be sequence controlled by a control circuit (not shown) and, by pulling a trigger 19 provided in the grip portion 2a of the housing 2 shown in FIG. 3, the wire feed device 3 and wire twisting device 4 are allowed to execute one cycle operation which consists of a wire feed step and a wire twisting step.
In operation, if the trigger 19 is pulled, then a wire feed motor (not shown) is firstly actuated to rotate the feed roller 5, thereby feeding the wire W to the nose portion 7; and, the wire W is curved in an arc manner along the shape of a guide groove formed in the inner periphery of the nose portion 7 and is then wound around the peripheries of the reinforcements R in a loop manner. If a given number of windings of the wire W are finished, then the wire feed motor is caused to stop and, following this, the motor 8 of the wire twisting device 4 is started.
FIG. 4 shows the twisting operation of the wire twisting device 4. At the wait/ready position of the wire twisting device 4 shown in FIG. 4 (a), a rotation prevention pawl 20 is in engagement with the rotation prevention fin 17 of the sleeve 16 and, therefore, the sleeve nut 15, sleeve 16 and shaft 11, respectively are kept against rotation.
And, in this state, if the screw shaft 10 is driven or rotated counterclockwise when viewed from the motor 8 side (in FIG. 4(a), the right side), then the sleeve nut 15 and sleeve 16 are moved forward in an integral manner. As shown in FIGS. 4(b), (c) and (d), at the same time when the sleeve 16 starts to move forward, the hook levers 18 are respectively rotated in their closing directions due to the cam actions of the guide pin 14 and guide grooves 18a to thereby grip the wire loop and, after then, as shown in FIG. 4(e), the hook levers 18 cross each other completely. And, due to the forward movement of the sleeve 16, the fin 17 of the sleeve 16 is removed from the engagement with the rotation prevention pawl 20, thereby allowing the sleeve nut 15, sleeve 16 and shaft 11 to rotate together with the screw shaft 10, with the result that the wire loop gripped by the hook levers 18 can be twisted and bound.
After then, a rotary type of shearing device 21, which is provided in the wire path of the nose portion 7 shown in FIG. 3, is driven to thereby cut the wire within the nose portion 7 and, at the same time, the motor 8 is reversed to thereby move back the sleeve nut 15 and sleeve 16, so that the hook levers 18 are spread open to thereby release the wire; and, the wire twisting device 4 returns back to the wait/ready position.
Because the wire W used in the above-mentioned reinforcement binding machine is wound around the reel, the outer peripheral portion of the wire W and the inner peripheral portion of the wire W are different in the winding curvature from each other. Therefore, when the wire W is drawn out from the nose portion 7, the curvature of the wire W is caused to vary due to such different winding curvatures of the outer and inner peripheral portions of the wire W. That is, at the time when the wire W is used initially, there is formed a wire loop of a relatively large diameter but, as the wire W is consumed, the diameters of the wire loops decrease sequentially and gradually. The loop diameter is also caused to vary depending on the tensile strength of the wire itself. A wire having a high tensile strength provides a large loop diameter.
The wire twisting device 4 is structured to have a back-and-forth stroke which allows the hook levers 18 to grip the wire loop even when the loop diameter varies to a certain degree. However, when the above-mentioned causes of loop diameter variance combine together, the curvature of the wire played out from the nose portion 7 can be excessively large, which may cause the leading end of the wire to collide with the leading end portion of the shaft 11. When such collision occurs, the running path of the wire can be deviated from too greatly to form a loop.
On the other hand, if the whole of the wire twisting device 4 is displaced backward in position in order to prevent the occurrence of such collision between the wire and the leading end face of the shaft 11, then there is raised a fear that, when the loop diameter of the wire decreases, the leading ends of the hook levers 18 are not able to reach the wire and thus they are unable to grip the wire loop.
Thus, there arises a technical problem which must be solved in order to improve the reliability of the conventional reinforcement binding machine.